SE Unit 1

SOFTWARE
ENGINEERING
UNIT 1: Need for Software Engineering

Need for Software Engineering
 Software is more
than just a program
code. A program is an
executable code,
which serves some
computational
purpose.
 Software is considered
to be a collection of
executable
programming code,
associated libraries and
documentations.
Software, when made
for a specific
requirement is called
software product.

 Engineering on the other hand, is all about developing products,
using well-defined, scientific principles and methods.
 IEEE defines “The application of a systematic, disciplined,
quantifiable approach to the development, operation and
maintenance of software.”
 A small program can be written without using software engineering
principles.
 But if one wants to develop a large software product, then software
engineering principles are absolutely necessary to achieve a good
quality software cost effectively.

 CHARACTERESTICS OF GOOD SOFTWARE
 A software product can be judged by what it offers and
how well it can be used
 Operational
 Transitional
 Maintenance

 Operational
This tells us how well software works in operations. It can be measured on:
 Budget
 Usability
 Efficiency
 Correctness
 Functionality
 Dependability
 Security
 Safety

 Transitional
 This aspect is important when the software is moved from one platform to
another:
 Portability
 Interoperability
 Reusability
 Adaptability

 Maintenance
 This aspect briefs about how well a software has the capabilities to
maintain itself in the ever-changing environment:
 Modularity
 Maintainability
 Flexibility
 Scalability

Size factors
 The major goal of software engineering is to provide tools
and techniques to increase the productivity of the available
software engineers.
 Total effort Devoted to software
 Distribution of Effort
 Project size categories

Size factors
 Project size is a major factor that determines the level of
management control and the types of tools and techniques
required on a software project.
 Trivial Project
 Small Project
 Medium Size Projects
 Larger Size Projects
 Very Large Projects
 Extremely large Projects

Size factors
 Trivial Project:
 No.of programmers : 1
 Duration :for a few days, few weeks
 Product Size :500 source line
 Packaged in :10 to 20 subroutines
 These Programs are often personal software

Size factors
 Small Project:
 No.of programmers : 1-5
 Duration : 1 to 6 months
 Product Size : 1000 to 2000 source lines
 Packaged in 25 to 50 subroutines
 Small Programs usually have no interactions with other programs.
 Example, Scientific applications written by engineers to solve
numerical problems.

Size factors
 Medium Size Projects:
 No. of Programmers : 2 to 7
 Duration : 1 to 2 years
 Product Size : 10,000 to 15,000 source lines
 Packaged in 250 to 1000 routines.
 Examples
 Medium size projects includes assemblers, Compilers, Small
management information system, inventory system and Process control
applications.

Size factors
 Larger Size Projects:
 o No.of Programmers : 5 to 20
 o Duration : 2 to 3years
 o Product Size :50,000 to 1 lakhs source lines.
 o Packaged in several sub systems.
 o Large programs has significant interactions with other programs and
sub
 systems.
 o Examples, Compilers, Small time sharing systems, database
packages, graphic packages and real time control systems.

Size factors
 Very Large Projects:
 o Duration : 4 to 5 years
 o Product Size : 1 million source lines
 o It consists of several major subsystem each of which forms a large
system.
 o The subsystem have complex,interactions with one another and with
other
 separate we developed system.

Size factors
 Extremely large Projects:
 o Duration : 5 to 10 years
 o Product Size : 1 million to 10 million source lines
 o It consist of several very large subsystem.
 o It involves real time processing, tele communications, multi tasking
and
 distributed processing.

Quality and Productivity Factors
 Development and maintenance of software
product are complex task.
 There is a fundamental difference between writing
a small programs for PC and developing or
modifying a software product.
 Software Quality and programmer productivity
can be improved by improving the process used
to develop and maintain software products.

Quality and Productivity Factors
 Individual Ability
 Team communication
 Product complexity
 System Level Programs
 Appropriate Notations
 Systematic Approaches
 Level of Technology
 Level of Reliability
 Problem Understanding
 Available Time
 Required Skill
 Facilities and
Resources
 Adequacy of Training
 Management Skills
 Appropriate Goals
 Raising Expectations

Individual ability
 Production and maintenance of software products are labor intensive activities.
 Productivity and Quality are direct functions of individual ability and effort.
 •There are two aspects of ability
• General competition of the individual
• Familiarity of the individual with the particular application area.
 Lack of familiarity with the application area can lead to low productivity and poor quality.
 On very large and extremely large projects no of programmers is so large.
 The individual differences in programmer productivity will tend to average out.
 Modules developed by weaker programmers may show poor quality and may lag in
delivery time.
 Small and medium size projects (5-fewer programmers) are extremely sensitive to the
ability of the individual programmer.

Team communication
 Programming has regarded as an individual and private activity.
 •
Programmers are rarely preceed as public documents and they rarely discuss the exact
details of the work in a systematic manner.
 •
So as a result ,the programmers may misunderstand the role of their modules in an
evolving system.
 •
This mistakes that may not be detected until some time later.
 Many of the recent innovations in software Engineering such as design, reviews and code
reading exercise have the goals of making software more visible and improving
communications among programmers.
 •Increasing product size results in decreasing programmer productivity due to the
increased complexity of interactions among program components.
 •Due to this increased communication is required among programmers, managers and
customers.

Team communication
 From Brooks observation:
 No of communication path among programmers = n(n-1)/2
 where, n=no of programmers.

 Increasing the number of team members from 3 to 4 to 5 increases the no of
communication path from 3 to 6 to 10.

 Brooks law:
 “Adding more programmers to a late project may make it later”

Product complexity
 There are 3 levels of product complexity.
 1. Application Programs
 2. Utility Programs.
 3. System level Programs
 Application Program: It includes scientific and data processing routines written in a high
level language such as COBOL,FORTRAN,C,C++.
 Utility Program: It includes compilers,Assemblers,linkage Editors and loaders. They may
be written in high level language or Assembly language.
 System Level Programs: It includes data communication packages real time process
control system, OS routines in any kanguages.(i.e)high level or assembly.

Product complexity
 Application programs have the highest productivity and the system programs the
lowest productivity.
 •
Utility programs can be produced at a rate of 5-10 times of system programs.
 •
Application programs at a rate of 25-100 times of system programs.
 •
A product that is twice as large or twice as complex as a known product, by
whatever measure other than effort may require 10 times or even 100 times the
amount of effort required for the known product.

Appropriate Notations
 •
In software engineer the representation schemes have fundamental
importance, programming languages provides compact notations for the
implementation phase of software development.
 •
But there are no widely accepted notations for stating functional requirements
,design specifications, test plans are performance criteria.
 •
There are no universally accepted notation in software Engineering.
 •
Appropriate notations provide vehicles of communication among project
personnel.
 •
It introduces the possibility of using automated software tools to manipulate the
notations and verify proper usage.

Systematic Approaches
 •In every field there are certain accepted procedures and techniques
 •A Single approach to software development and maintenance will not be adequate
to cover all situations.
 • In the evaluation of software engineering it is not clear which of the various
approaches to software development should be used in which situation.
 •The flexibility of software is a great strength and also a great source of difficulty in
software engineering.
 • Requirements can also change due to poor understanding of the problem are
external economic and political factors beyond the control of the customers or
developers.
 •Notations and procedures provide the ability to trace and access the impact of
proposed changes are necessary to make visible the true cost of apparently small
changes to source code.
 •Use of appropriate notations and techniques makes control change possible without
degrading the quality of work products.
 •Planning for software project must include plans for change control.

Level of Technology
 It include factors such as programming language, Machine Environment,
The Programming Practices and Software tools
 Modern Programming languages provide improved facilities for data
definition and data usage.
 Improve Constructs for specifying control flow, better modularization
facilities, user defined exception Handling and facilities for concurrent
programming.
 The machine environment includes a set of hardware and software facilities
for developing, using and maintaining a software product.
 Modern programming practices include use of systematic Analysis and
design techniques, notations ,structure coding, systematic techniques for
designing and documenting and testing.

Level of Reliability
 Every software product must possess basic level of reliability.
 Extreme reliability is gained only with great care in analysis, design,
design implementation, system testing and maintenance of software
product.
 Both human and machine resources are required to obtained
increased reliability.
 Problem Understanding:
 Failures to understand the true nature of the problem to be solved is
a common and difficult issue.

Available Time
 Often the customer does not truly understand nature of the problem.
 Often the software engineering does not understand the application area and has trouble
communicating with the customer because of differences in educational backgrounds view the
points and technology.
 Careful planning, customer interviews, task observations and prototyping, preliminary version of
the user’s manual and precise product specification can increase both customer and developer
understanding of the problem to be solved.
 Software projects are sensitive not only to total effort but also to elapsed time and the no. of
people involved
 Utilizing 6 programmers for 1 month will be less effective than using 1 programmer for 6 months.
 This is because the learning curve for 6 programmers on an 1 month schedule will occupy a large
percentage of the elapsed time and because the effort required for co-ordination and
communication among 6 programmers.
 Programmer Productivity is also sensitive to the calendar time available for project completion.
 Determining optimum staff in levels and proper elapsed times for various activities in software
product development is an important and difficult aspects of cost and resource estimation.

Required Skill
 Software Engineering requires a vast range of skills.
 o Good Communications
 o Knowledge of application area
 o Requirement definition and design
 o Problem solving skills
 o Implementation of software (i.e) Good programming knowledge, no
syntax error
 o Debugging and test plans
 o Inter personnel communication skill.

Facilities and Resources
 •
Work related factors such as •
Good machine access and quiet place to
work are more important.
 •
Software project managers must be effective in dealing with the resources
availability.

Adequacy of Training
 •
Factors that motivate the programmers to maintain high product quality,
high programmer productivity and high job satisfaction.
 Express oneself clearly in English
 •
Develop and Validate software requirements and design specifications.
 •
Work within application area
 •
Perform software maintenance
 •
Perform economic analysis.
 •
Work with project management techniques
 •
Work in groups

Management Skills
 •
Many of the problems in software project management are
unique.
 Managers experienced in management of computer hardware
projects find software project management to be difficult.
 This is due to the differences in design methods, notations
and development tools.
 Many Organizations offer project management training to
software engineers to prepare them for project management
task.

Appropriate Goals
 Primary Goal of software engineering is to development of
software products for their intended use.
 Every software product must provide optimal level of
 1. Generality
 2. Reliability
 3. Efficiency

Raising Expectations
 There are two interrelated aspects of raising expectations
 1.How much functionality, reliability and performance can be
provided by a given amount of development effort.
 2.Issues of fundamental limitations of software technology.

Managerial Issues
 Success of Software project involves
 Technical Activities
 Managerial Activities
 •Managers Control
 1.Resources
 2.Environment
 •Important managers responsibility
 Software product delivered on time
 Software working according to customer’s wish
 Software within cost estimates

Managerial Issues
 Other managerial
responsibility:
o Business Plans
o Recruiting customers
o Developing Marketing
Strategies
o Recruiting and training
employees
 Important Problems:
 •
Planning in poor selection for project
managers are poor (i.e) Procedures
and Techniques
 •
Description of project is poor
estimation of resources for software
project is poor
 •
Success criteria is inappropriate
decisions rules are poor(for selecting
the proper organizational structure,
correct management techniques )
 •
Procedures ,methods and
techniques are not readily available.

Managerial Issues: Methods for solving these
problems
 Educate and Train
 Top management
 Project
 Software developers
 •
Analyze the data from previous software project to find effectivemethods
 •Define objectives, quality
 •Establish success priority criteria
 •Develop accurate cost and schedule that are accepted by management and
customer
 •Selection of project managers
 •Specific work assignments to software developers

Planning a Software Project
 •Goals can be formulated using concise statement ,constraints.
 •Goal apply to both development process and work product.
 •It can be either qualitative or quantitative.
 •Every development process should provide product on time within cost
estimates .
 •Opportunities for project personnel to learn new skill.
 Requirements includes:
 •Functional requirements
 Performance
 •Requirements for hardware, software and firmware.

 Definition - problem
 1. Develop a definitive statement of the problem to be solved, Include a
description of the present situation, problem constraints and a statement of the
goals to be achieved. The problem statement should be phrase in the customer's
terminology.
 2. Justify a computerized solution strategy for the problem.
 3. Identify the functions to be provided by, and the constraints on, the hardware
subsystem, the software subsystem and the people subsystem.
 4. Determine system level goals and requirements for the development process
and the work products.
 5. Establish high-level acceptance criteria for the system.

 Solution Strategy
 6. Outline several solution strategies, without regard for constraints.
 7. Conduct a feasibility study for each strategy.
 8. Recommend a solution strategy, indicating why other strategies were rejected.
 9. Develop a list of priorities for product characteristics.

 Planning the development process
 10. Define a life-cycle model and an organizational structure for the project.
 11. Plan the configuration management quality assurance and validation
activities.
 12. Determine phase-dependent tools, techniques and notations to be used.
 13. Establish a preliminary cost estimates for system development.
 14. Establish preliminary development schedule.
 15. Establish preliminary staffing estimates.
 16. Develop preliminary estimates of the computing resources required to
operate and maintain the system.
 17. Prepare a glossary of terms.
 18. Identify sources of information, and refer to them throughout the project plan.

Factors to Consider in Project Planning
 1. Estimation techniques to be used; accuracy required.
 2. Life-cycle model, control functions and reviews
 3. Organizational structure
 4. Level of formality in specification, test plans etc.
 5. Level of verification and validation
 6. Level of configuration management required.
 7. Level of quality assurance required
 8. Follow-on maintenance responsibilities
 9. Tools to be developed and used
 10. Personnel recruitment and training

Some factors to consider in setting
project goals
 1. New capabilities to be provided
 2. Old capabilities to be preserved/enhanced
 3. Level of user sophistication
 4. -Efficiency requirements
 5. Reliability requirements
 6. Likely modifications
 7. Early subsets and implementation priorities
 8. Portability requirements
 9. Securely concerns

Planning the development process
 The software life cycle includes all activities that are required to define,
develop, test. deliver, operate and maintain a software product.
 Different life-cycle models emphasize different aspects of the life cycle. No
single life-cycle model is appropriate for all software products.
 As the model provides a basis for categorizing and controlling the various
activities required to develop and maintain a software product it is important
to define a life-cycle model lor each software project.
 If all the members who are involved in a particular software project accept a
life-cycle model for it then it improves the project communication, enhances
project manageability, resource allocation cost control and product quality

 Analysis consists of two sub phases
 1. Planning
 2. Requirements definition
 The products of planning are
 1. System Definition & 2. Project plan

 Format of a system definition
 Section 1 Problem definition
 Section 2 System justification
 Section 3 Goals for the system and the project
 Section 4 Constraints on the system and the project
 Section 5 Functions to be provided (hardware/software/people)
 Section 6 User characteristics
 Section 7 Development / operating / maintenance environments
 Section 8 Solution strategy
 Section 9 Priorities for system features
 Section 10 System Acceptance criteria
 Section 11 Sources of information
 Section 12 Glossary of term

Planning the development Process -
Format for project plan
 Life-cycle model
 Terminology / milestone / work products
 Organizational structure
 Management structure/team
Structure/Work breakdown
 structure/statements of work.
 Preliminary staffing and requirements
staffing and resource schedule.
 Preliminary development schedule PERT
network / Gantt charts
 Preliminary cost estimate .
 Project monitoring and control mechanisms.
 Tools and techniques to be used
 Programming languages
 Testing requirements
 Tools and techniques to be used
 Programming languages
 Supporting documents required
 Manner of demonstration and delivery
 Training schedule and materials
 Installation Plan
 Maintenance considerations
 Method and time of delivery
 Method and time of payment
 Sources of information

 Requirements definition is concerned with identifying the basic functions of
the software components in a hardware/software people system.
 The product of requirements definition is a specification that describes
 Processing environment
 The required software functions
 Performance constraints on the software (size, speed machine configuration)
 Exception handling Implementation priorities.

 Software design phase follows the analysis phase. Design phase
consists of
 1. Architectural design
 2. Detailed design
 Architectural design involves the identification of the software
components, by decoupling and decompiling the software components.
 Detailed design is concerned with the details of how to package the
processing modules and how to implement the processing algorithms,
data structures and interconnections among modules and data
structures.
 Detailed design involves adaptation of existing code, modification of
standard algorithms, invention of new algorithms, design of data
representations and packaging of the software product.

 Implementation phase follows the design phase. This phase consists of the following
sub phases.
 1. Code 2. Debug 3. Unit test
 Coding involves the translation of design specifications into source code Modern
programming languages provide many features to enhance the quality of the source
code.
 Errors discovered during the implementation phase may include errors in the data
interfaces between routines, logical errors in the algorithms, error in data structure
layout and failure to account for various processing cases.
 The source code may contain errors that reflect the failure to capture the customer's
requirements, design errors that reflect failure to translate requirements into design
specifications and implementation errors that reflect failure to correctly translate
design specifications into source code.
 Unit test involves the testing of each and every processing module whether it works
correctly for the given test data.
 After writing the source code (i.e. after the implementation phase), the software

 Testing involves the following two activities.
 1. Integration testing 2. Acceptance testing
 In order for the whole software system to function
correctly, the modules are to be integrated. Careful
planning is needed to improve the availability of the
modules for the integration when needed.
 Acceptance testing involves planning and execution of
various types of tests in order to demonstrate that the
implemented software system satisfies the
requirements state in the requirements document.

 The software system is released for the production work after
being accepted by the customer and it enters the maintenance
phase of the following activities.
 1. Enhancement 2. Adaptation 3. Fix
 Enhancement involves the improvement of the capabilities of
the software system. Adaptation is making the software system
suitable for new processing environments. Fixing involves the
correcting of the software bugs.

Planning an Organization Structure
 The tasks that are performed during the lifetime of a software
product include planning, product development, services,
publications, quality assurance, support and maintenance.
 The Planning task identifies external customers and internal
product needs, conducts feasibility studies and monitors
progress from beginning to end of the product life cycle.
 Project Structure
 Programming team structure
 Management by objectives

 Project format
 Use of project format involves assembling a team of programmers who
conduct a project from start to finish.
 Project team members do the product definition, designing, implementation,
testing, conduct the project reviews and prepare the supporting documents.
 After completing thee phases some of the team members will stay with the
product during installation and maintenance while others will be moved on
to a new project.
 They too have the responsibility for the maintenance of the delivered
product.

 Functional format
 In functional format a different team of programmers performs
each phase of the project.
 The team members performing one particular phase generate
the work products for that phase. It is then passed on to the
next team who in turn generate the work products for. the
phase.

 The various teams along with the function performed by them and the work products
generated by them
 1. Planning and Analysis team System Definition and Project Plan
 2. Product Definition team Performs software requirements analysis
and
prepares Software Requirements Specification
 3. Design team Designs the product to confirm with the
System Definition and
Requirement Specification
 4. Implementation team Implements, debugs and unit tests the
product
 5. System testing team Does the integration testing and acceptance

 Programming team structure
 Every programmer team must have an internal structure.
 The best structure for a particular project depends on the nature of the project and
the product and on the characteristics of the individual team members.
 1. Democratic teams
 2. Chief programmer teams
 3. Hierarchical team

 Democratic teams
 All the team members participate in all decisions. The idealized democratic
team structure is also called as an "egoless team".

 In an egoless team, goals are set and decision are made by group consigns.
 Groups leadership is moved from one member to the other based on the activity and the capability of the
team members.
 Advantages of the democratic team includes :
 1. Opportunity for each team member to contribute to decisions
 2. Team members can learn from one another
 3. Involvement in the project is increased as the team members are participating in each and every activity of
the team.
 4. As the problem is discussed in an open, nonthreatening work environment, the job satisfaction is higher in
the democratic team.
 Disadvantages.
 1. Decision-making in the critical situations are difficult as it requires the agreement of all the team members.
 2. Co-ordination among the team members is essential

 Chief Programmer Teams
 Chief programmer teams are highly structured.
 A team of programmers work under the chief programmer. The chief programmer designs the
product, implements critical parts of the products and makes all major technical decisions.
 Work is allocated to the programmers by the chief programmer. The programmers write code,
debug, document and unit test it.

 Chief programmer teams are effective in two situations
 first, in data processing applications where the chief programmer has
responsibility for sensitive financial software packages and the packages
can be written by relatively unskilled programmers
 second, in situations where one senior programmer and several junior
programmers are assigned to a project.
 In the latter case, the chief, the chief programmer team structure is used to
train the junior programmer and to evolve the team structure into a
hierarchical or democratic team when the junior programmers have
obtained enough experience to assume responsibility for various project
activities.

 Hierarchical team structure
 The hierarchical team structure occupies a middle position between the
extremes of democratic items and chief programmer teams.

 Each major subsystem in the hierarchy can be assigned to a team
 The team leaders will report to the project leader.
 For effective communication and supervision of work activities, the number
of immediate subordinates at each level must be limited to five to seven
people.
 A large project may have several levels in the hierarchy.
 Disadvantage:
 The competent and experienced programmers may be promoted to
management positions. Even though higher salary and prestige are
associated with higher positions, the promotion may have doubly negative
effect of losing a good programmer and creating a poor manager. The
competent programmers need not have a good communication skill and

 Management by objectives
 Depending upon the nature of the software project, project format and team
structure are identified.
 After identifying the project format and team structure, the project leader
has an important responsibility of controlling the various activities of the
team members.
 It is necessary for a project leader to establish methods for directing and
controlling the activities of individuals assigned to the project.
 At the beginning of the project, project members develop their
understanding of the project and their role in the project.

 Using MBO, the project members set their own goals and objectives with
the help of their supervisor, participate in settling of their supervisor's goal
and they are evaluated.
 Management by objectives can be applied at all levels of an organization,
and can include product oriented objective uch as completion of design or
testing and self-improvement objectives such as skills to acquire and
preparations for advancement.
 Disadvantages
 1. Employees are required to state excessive number of objectives (20 or
30)
 2. The reporting period is too long (6 months or more)
 Objectives of software projects should be specific, few in number and

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